The present invention relates to a collapsible metal tube and aerosol can whose inside wall surface is covered with a highly reliable dense resin film that is virtually devoid of pinholes, excellent in elongation at break, and devoid of cracks or other defects caused by folding and other types of deformation; and to a method for manufacturing a collapsible metal tube.
Collapsible metal tubes from which a paste stored therein is squeezed when the body portion is subject to plastic deformation by pressure have been used to store various foodstuffs, drugs, cosmetics, and the like.
A collaspsible metal tube comprises a body portion composed of metal walls susceptible of plastic deformation, and a shoulder portion and mouth/neck portion connected to one end of the body portion. The other end of the body portion of the collapsible metal tube is sealed by folding and tightening or the like, and the mouth/neck portion is openably closed with a cap.
In such collapsible metal tubes, the metal component of the body portion, or the outside air and moisture (water vapor) entering bit by bit over a long period of time through the fold formed at one end should be prevented from spoiling the contents, while the contents should be prevented from corroding the metal body portion. It has already been proposed in the past to use as such collapsible metal tubes so-called double-tube collapsible tubes, which is obtained by inserting a resin tube having an essentially complementary shape into a metal tube open at one end, packing the contents therein through the open end of the resin tube, and sealing the open end by applying pressure and heat through the metal tube to heat-seal. Problems with such a double-tube type of collapsible metal tube are that a large number of operations are required, it is difficult to align the outer metal tube or cylinder and the inner resin cylinder and to adjust the difference in the dimensional tolerance therebetween, and so forth. In addition, it leads to an inevitable increase in production costs to manufacture such tubes, and they can therefore be used in a very limited applications. Another disadvantage of such collapsible tubes is that it is difficult to remove the contents completely because the internally mounted resin tube tends to restore its original shape due to its thickness and elasticity.
It has also been proposed to use collapsible metal tubes in which a thermosetting resin coating material is sprayed on the inside wall surface of the body portion, and the resulting layer is heated and cured to obtain a thermosetting resin coating such as an epoxy phenolic resin film or a phenol butyral resin film. In such thermoplastic resin films, however, it is virtually impossible to prevent both the formation of pinholes and the formation of cracks by folding and other types of deformation.
That is, thermosetting resins are commonly rigid and are likely to be suffered from cracks or the like when subjected to folding or other types of deformation. This tendency to form cracks is even more pronounced when the film thickness is 15 xcexcm or greater. An additional problem is that coating defects are formed by air bubbles and the like in thermosetting resin coatings during the formation of coatings, and pinholes tend to form in the resin films obtained by heating and curing such films. The pinhole formation becomes even more pronounced when an attempt is made to significantly reduce the thickness of a thermosetting resin film in order to prevent cracking. The pinhole formation can be reduced to some extent by reapplying the coating, but repeated application complicates the coating formation process, and when the number of application cycles is sufficient to achieve a complete elimination of pinholes, the total film thickness results in 20 xcexcm or greater. It is therefore difficult to perform a sufficient number of application cycles in order to prevent the formation of coating defects while keeping the film thickness within a range to cause few cracks.
In other words, commonly used collapsible tubes with thermosetting resin coatings having a thickness of 5 to 15 xcexcm are such that (1) it is difficult to prevent pinholes from forming in the resin films and that (2) when the thickness of a resin film is increased to 20 xcexcm or greater in order to prevent pinhole formation, it is impossible to prevent cracks from being formed by folding or other types of deformation, with the result that the quality of the contents or metal body portions declines in both cases. The thermosetting resin coatings of conventional collapsible tubes still have a room for being improved in their ability to protect the contents or metal body portions.
In the collapsible metal tubes having thermosetting resin films on the inside wall surfaces of their body portions, it is necessary to coat the inside wall in the area of the open end with an end sealant such as a rubber latex in order to preserve the airtightness during the stage following the heating and curing for obtaining the thermosetting resin film and the subsequent introduction of the contents through the open end, that is, during the stage when the open end (cuff) is folded and tightened. The resulting disadvantage of such collapsible metal tubes is that the folding and tightening processes are too complicated to keep productivity.
Similar to collapsible metal tubes, aerosol cans serve as containers that have body portions consisting of metal walls. Normally, an aerosol can has a bottomed cylindrical body portion consisting of metal walls, a shoulder portion and neck portion connected to the upper end of the body portion, and a valve assembly provided to the neck portion. A drug or cosmetic that is stored in the aerosol can together with pressurized gas or another propellant is ejected outside through the valve assembly by the action of the valve assembly.
In such aerosol cans as well, the metal components of the body portion should be prevented from spoiling the contents while for the contents should be prevented from corroding the metal body portion. In the past, resin films consisting of epoxy phenolic resins, epoxy urea resins, vinyl organo-resins, fluororesins (polytetrafluoroethylene, polyperfluoroethylene, and the like), polyamides (nylon-12 and the like), polyesters (polyethylene terephthalate), polyethylenes and the like were formed on the inside surfaces of body portions and bottom portions.
Even in such resin films, however, coating defects formed due to the air bubbles and the like present in the films during the formation of coatings, and pinholes are apt to form in the resulting resin films. The pinhole formation can be reduced to some extent by repeatedly applying the coating, but repeated application is disadvantageous in that it complicates the coating formation process and lowers the productivity.
The present invention has been accomplished in order to overcome the aforementioned disadvantages associated with prior art. An object of the present invention is to provide a collapsible metal tube whose inside wall surface is coated with a highly reliable dense resin film that is virtually devoid of pinholes, excellent in elongation at break, devoid of cracks or other defects caused by folding and other types of deformation, and excellent in ability to protect the metal body portion and the contents; and to provide a method for manufacturing such a tube.
Another object of the present invention is to provide an aerosol can whose inside wall surface is coated with a dense resin film that is virtually devoid of pinholes and that has an excellent ability to protect the metal body portion and the contents.
Yet another object of the present invention is to provide an apparatus capable of performing a method for manufacturing the collapsible metal tube pertaining to the present invention.
The collapsible metal tube according to the present invention comprises:
a metal body portion plastically deformed without difficulty, said body portion being sealed at one end,
a shoulder portion and a mouth/neck portion connected to the other end of the body portion, and
a resin film provided on the inside wall surface of the body portion, said resin film comprising a metal-adhesive thermoplastic resin layer formed by spray-coating the inside wall surface of the body portion with a dispersion of fine spherical particles of a metal-adhesive thermoplastic resin and then heating to fuse these particles.
The resin film of the collapsible metal tube according to the present invention is not limited in terms of its layer structure as long as this film has a metal-adhesive thermoplastic resin layer. The resin film, therefore, comprises at least one such metal-adhesive thermoplastic resin layer. It is also possible for the resin film to comprise a metal-adhesive thermoplastic resin and a thermoplastic resin layer capable of adhering to this metal-adhesive thermoplastic resin layer, or a thermosetting resin layer in contact with the surface of the metal body portion and a metal-adhesive thermoplastic resin layer formed on the inside of the thermosetting resin layer.
The method for manufacturing the collapsible metal tube according to the present invention comprises:
spray-coating a dispersion of fine spherical particles of a metal-adhesive thermoplastic resin on the inside wall surface of a metal body portion open at one end of a collapsible tube comprising the metal body portion plastically deformed without difficulty, and a shoulder portion and a mouth/neck portion connected to the other end of the body portion in this order, to form a coating of uniform thickness and heating the coating to fuse the fine spherical particles of the resin, thereby forming a metal-adhesive thermoplastic resin layer.
The coating apparatus according to the present invention is an apparatus capable of manufacturing the collapsible metal tube described above which comprises:
a coating unit equipped with a nozzle having at its tip a coating material spray orifice for spraying the inside wall surface of a cylindrical article open at least one end with a coating material, said nozzle being capable of moving in the direction of the major axis of the metal cylinderical article to be coated; and
a drive unit for making a relative motion between the coating material spray orifice of the coating unit and the inside wall surface of the cylindrical article in such a manner that the inside wall surface of the cylindrical article moves around the spray orifice in a direction of approximately the circumferential direction.
The aerosol can according to the present invention comprises: a bottomed cylindrical body portion; a shoulder portion and a mouth/neck portion connected to the other end of the body portion; a valve assembly provided to the mouth/neck portion; and a resin film comprising a metal-adhesive thermoplastic resin layer, said resin film being prepared by spray-coating the inside wall surface of the body portion with a dispersion of fine spherical particles of a metal-adhesive thermoplastic resin and then heating and fusing these particles.